Screws are indispensable tools widely used with screw drivers. They are also commonly used fastening tools ubiquitously adapted from very small articles to large machineries and buildings, such as ornamental items and vehicles and architectures. They play important roles in the life and work of mankind.
Conventional screws used on wood or building materials generally have a sharp end to bore into an article through the surface thereof and threads tightly wedged in a hole formed by the sharp end to produce an internal thread by fracturing and thrusting the working piece, and then form a tight fastening by wrenching helically.
The threads of the conventional screw usually are formed on the periphery thereof in a symmetrical manner. During drilling process, resistance gradually increases with sinking insertion of the threads. While the resistance takes place during the sharp end sinking and threads thrusting on the working article such as wood or structural material, a friction also occurs while the threads move forwards. In addition, debris and powders generated in the drilling process will also increase the friction. Hence a greater force is needed to perform the drilling process as the screw is sunken deeper.
To facilitate drilling process by using the screw, many automatic tools have been developed. However, these tools make user's discerning the screw conditions more difficult. For instance, it is not easy to detect increase of resistance, and an excessive force could be exerted and result in fracturing of the screw. This causes resource waste or even bouncing away of the screw that could create hazardous conditions to users.